Techniques For Detection Of Explosives Research Articles

Detection of Explosive Residues Using Nanomaterial-based Sensors: A Review

Abstract: Due to the recent rise in explosive-based terrorism and ecological issues, the invention of good capacity detectors for the identification of explosives has emerged as one of the major thirsts in the scientific community. Due to their unique optical and electrical properties, nanocomposites can meet all of the prerequisites for developing preferential, responsive, easy, and cost-effective sensor nodes for the sensing of various explosives. This study primarily throws light on current developments in explosives detection using nanomaterial-based sensors. In particular, it describes how quantum dots, carbon nanomaterials, monometallic nanomaterials, and bimetallic nanomaterials have been used to detect explosives optically and electrochemically. The accurate and consistent features of the nanomaterials, including their synthesis, the explosive detection technique, and the analytical facets, are all thoroughly examined.

A Mathematical Model for Sublimation of a Thin Film in Trace Explosive Detection Problem.

Here, we introduce an advanced mathematical model for the sublimation of thin films of explosives. The model relies on the Hertz-Knudsen-Langmuir (HKL) equation that describes the vaporization rate of an explosive and controls the mass exchange between the surface and the ambient air. The latest experimental data on sublimation and diffusion of 2,4,6-trinitrotoluene (TNT) monocrystals were factored in, as well as the data on the sublimation rate of hexogen (RDX), octogen (HMX), and picramide (TNA) traces. To advance the mathematical model we suggested previously, we took into account the structure of a substrate on which a thin explosive layer was deposited. The measurement problem of the sublimation rate and limits of an explosive arises from developing and advancing remote detection methods for explosives traces. Using mathematical modelling, we can identify a detectable quantity of a specific explosive under given conditions. We calculated the mass of the explosive in the air upon sublimation of thin explosive films from the surfaces over a wide range of the parameters in question and made conclusions regarding the application limits of the devised standoff trace explosive detection techniques.

Explosive detection and identification using X-ray fluorescence and thermal fingerprint of silica encapsulated nanoparticles

This paper describes a nanoparticle-based explosive’s marking technique for pre-blast detection and post-blast identification of explosives. Trace explosive containing a panel of metallic nanoparticles (metals and alloys) can be detected by nanoparticles’ characteristic X-ray fluorescence, and identified by their unique thermal properties (i.e., composition dependent melting temperatures and discrete and sharp melting peaks in differential scanning calorimeter). The selected nanoparticles added into explosive are easy to manufacture and safe to use, do not affect explosive performance, can survive blast, thus will greatly reduce threats of unlawful uses of explosives.

Two-Dimensional Electrochemiluminescence on Porous Silicon Platform for Explosive Detection and Discrimination.

This work established a rapid and sensitive explosive detection and recognition technique. We report a two-dimensional electrochemiluminescence (2-D ECL) method based on porous silicon (pSi) by monitoring the dynamic change in peak position and peak intensity of pSi-ECL. Gold nanoparticles (AuNPs) were deposited on the pSi surface to promote the electrochemical reaction and electron transfer efficiency at the pSi-electrolyte interface. The 2-D ECL can effectively detect and discriminate different classes of explosives including nitro compounds, peroxides with nitrogen atoms, and peroxides without nitrogen atoms due to their different oxidation and electron transfer ability.

A survey in wireless sensor network for explosives detection

Explosive detection techniques are one of the most important modern technologies for saving civilian lives from terrorist operations. Technological advances and the development of explosive detection have greatly reduced the proportion of terrorist operations around the world. One of the most modern technologies that assist in the detection of explosives is the use of wireless sensor network. In this paper, modern practical studies of the wireless sensor network in explosives detection field have been taken into consideration and statistics are being conducted on these studies. Explosive detection requires the use of special sensors and compatible to work with the wireless sensor network. This paper deals with three main axes in wireless sensor systems: first axes is the scalability of wireless sensors in explosives detection technology. Second axes of WSN explosives detection system is the communication and mobility of these networks and sensors. The latest axes discuss the data security of the wireless sensor network used in the process of detecting explosives and the potential dangers that the system can direct in terms of data security.

Photo-vibrational spectroscopy of solid and liquid chemicals using laser Doppler vibrometer.

Photoacoustic/photothermal spectroscopy is an established technique for trace detection of chemicals and explosives. However, prior sample preparation is required and the analysis is conducted in a sealed space with a high-sensitivity microphone or a piezo sensor coupled with a lock-in amplifier, limiting the technique to applications in a laboratory environment. Due to the aforementioned requirements, traditionally this technique may not be suitable for defense and security applications where the detection of explosives or hazardous chemicals is required in an open environment at a safe standoff distance. In this study, chemicals in various forms (membrane, powder and liquid) were excited by an intensity-modulated quantum cascade laser (QCL), while a laser Doppler vibrometer (LDV) based on the Mach-Zehnder interferometer was applied to detect the vibration signal resulting from the photocoustic/photothermal effect. The photo-vibrational spectrum obtained by scanning the QCL's wavelength in MIR range, coincides well with the corresponding spectrum obtained using typical FTIR equipment. The experiment demonstrated that the LDV is a capable sensor for applications in photoacoustic/photothermal spectroscopy, with potential to enable the detection of chemicals in open environment at safe standoff distance.

MEKC-UV as an effective tool for the separation and identification of explosives, high explosives, and their degradation products in environmental samples.

MEKC has been used in conjunction with UV detection for identification and quantitation of high explosives in environmental samples. To ensure the compatibility of the technique with ESI-MS, perfluorooctanoic acid (PFOA), a volatile micelle, was used. Separation of EPA Method 8330 Mixes A and B using various concentrations of the micelle showed that the 80 mM solution of PFOA was the optimum concentration for the separation of the explosives. MEKC analysis of explosives with ESI-MS under optimum micelle concentration provided excellent results indicating the compatibility of the method with ESI-MS. Finally, the MEKC-UV method was applied to the detection and quantitation of explosives in various environmental samples including water, sand, and soil. The results demonstrate that the MEKC method described herein is a viable technique for detection of explosives in environmental samples using UV detection, while maintaining the compatibility of the technique with MS detection without any modification to the separation method, if laboratories decided to pursue this route in the future.

Review of explosive detection methodologies and the emergence of standoff deep UV resonance Raman

Due to terrorist use of explosive devices, intense interest has been directed towards the development of techniques and instrumentation to detect explosives. A number of analytical techniques are currently under investigation for trace explosive detection. Several methods have been successfully commercialized including colorimetric kits, fluorescence quenching sensors, and ion mobility spectrometers that see widespread field use. A key limitation of all currently utilized field techniques is that they require close proximity or physical interaction with the object being analyzed. The ideal trace explosive detection technique would be able to detect trace amounts of explosives from a distance to ensure personnel safety. Laser‐based spectroscopies are the only currently viable techniques that can be utilized to sense trace amounts of explosives at standoff distances. This review compares currently used explosive detection techniques with recently developed standoff methods. We emphasize the development of UV resonance Raman spectroscopy for standoff explosive detection. This work has recently been enabled by advances in laser and spectrometer design. Trace explosive detection has also been advanced by the recently developed understanding of deep UV photochemistry for several explosive molecules. Copyright © 2016 John Wiley & Sons, Ltd.

Novel CE–MS technique for detection of high explosives using perfluorooctanoic acid as a MEKC and mass spectrometric complexation reagent

To address the need for the forensic analysis of high explosives, a novel capillary electrophoresis mass spectrometry (CE–MS) technique has been developed for high resolution, sensitivity, and mass accuracy detection of these compounds. The technique uses perfluorooctanoic acid (PFOA) as both a micellar electrokinetic chromatography (MEKC) reagent for separation of neutral explosives and as the complexation reagent for mass spectrometric detection of PFOA-explosive complexes in the negative ion mode. High explosives that formed complexes with PFOA included RDX, HMX, tetryl, and PETN. Some nitroaromatics were detected as molecular ions. Detection limits in the high parts per billion range and linear calibration responses over two orders of magnitude were obtained. For proof of concept, the technique was applied to the quantitative analysis of high explosives in sand samples.

Infrared photothermal imaging spectroscopy for detection of trace explosives on surfaces

We are developing a technique for the standoff detection of trace explosives on relevant substrate surfaces using photothermal infrared (IR) imaging spectroscopy (PT-IRIS). This approach leverages one or more compact IR quantum cascade lasers, which are tuned to strong absorption bands in the analytes and directed to illuminate an area on a surface of interest. An IR focal plane array is used to image the surface and detect increases in thermal emission upon laser illumination. The PT-IRIS signal is processed as a hyperspectral image cube comprised of spatial, spectral, and temporal dimensions as vectors within a detection algorithm. The ability to detect trace analytes at standoff on relevant substrates is critical for security applications but is complicated by the optical and thermal analyte/substrate interactions. This manuscript describes a series of PT-IRIS experimental results and analysis for traces of RDX, TNT, ammonium nitrate, and sucrose on steel, polyethylene, glass, and painted steel panels. We demonstrate detection at surface mass loadings comparable with fingerprint depositions ( 10μg/cm2 to 100μg/cm2) from an area corresponding to a single pixel within the thermal image.

Associated particle technique in single-sided geometry for detection of explosives

Associated particle technique (APT) for detection of explosives is well established but has been implemented mostly for fixed portal systems. In certain situations, a portable system is required where the suspect object cannot be moved from site. This paper discusses the development of a portable APT system in single-sided geometry which can be transported to site and requires only one-sided access to the object. The system comprised D-T neutron source and bismuth germanate (BGO) detectors fixed on a portable module. Different aspects of the system have been discussed such as background contribution, time selection, and elemental signatures. The system was used to detect benign samples and explosive simulants under laboratory condition. The elemental ratios obtained by analyzing the gamma spectra show good match with the theoretical ratios.

Development of ion mobility spectrometry and its application for detection trace explosives

Ion mobility spectrometry is widely used for detection of explosives in the field of airport and in the war against terror due to its satisfactory features: fast response, high sensitivity, good portability, easy operation, etc. This paper introduced the pricinple, classification and also their features of ion mobility sepctrometry; also mainly introduced recent developments of technique for detection of explosives in our laboratory including titration region-ion mobility spectrometry, new method to improve the resolution of ion mobility spectrometry and also the nonradioactive high-efficency ionization source based on VUV lamp. Finally, the development tendency and prospect of ion mobility spectrometry for detection of explosives was predicted.

Fast Switching of CO3–(H2O)n and O2–(H2O)n Reactant Ions in Dopant-Assisted Negative Photoionization Ion Mobility Spectrometry for Explosives Detection

Ion mobility spectrometry (IMS) has become the most deployed technique for on-site detection of trace explosives, and the reactant ions generated in the ionization source are tightly related to the performances of IMS. Combination of multiform reactant ions would provide more information and is in favor of correct identification of explosives. Fast switchable CO3(-)(H2O)n and O2(-)(H2O)n reactant ions were realized in a dopant-assisted negative photoionization ion mobility spectrometer (DANP-IMS). The switching could be achieved in less than 2 s by simply changing the gas flow direction. Up to 88% of the total reactant ions were CO3(-)(H2O)n in the bidirectional mode, and 89% of that were O2(-)(H2O)n in the unidirectional mode. The characteristics of combination of CO3(-)(H2O)n and O2(-)(H2O)n were demonstrated by the detection of explosives, including 2,4,6-trinitrotoluene (TNT), cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), ammonium nitrate fuel oil (ANFO), and black powder (BP). For TNT, RDX, and BP, product ions with different reduced mobility values (K0) were observed with CO3(-)(H2O)n and O2(-)(H2O)n, respectively, which is a benefit for the accurate identification. For ANFO, the same product ions with K0 of 2.07 cm(2) V(-1) s(-1) were generated, but improved peak-to-peak resolution as well as sensitivity were achieved with CO3(-)(H2O)n. Moreover, an improved peak-to-peak resolution was also obtained for BP with CO3(-)(H2O)n, while the better sensitivity was obtained with O2(-)(H2O)n.

Resonance-Enhanced Raman Spectroscopy on Explosives Vapor at Standoff Distances

Resonance-enhanced Raman spectroscopy has been used to perform standoff measurements on nitromethane (NM), 2,4-DNT, and 2,4,6-TNT in vapor phase. The Raman cross sections for NM, DNT, and TNT in vapor phase have been measured in the wavelength range 210–300 nm under laboratory conditions, in order to estimate how large resonance enhancement factors can be achieved for these explosives. The results show that the signal is enhanced up to 250,000 times for 2,4-DNT and up to 60,000 times for 2,4,6-TNT compared to the nonresonant signal at 532 nm. Realistic outdoor measurements on NM in vapor phase at 13 m distance were also performed, which indicate a potential for resonance Raman spectroscopy as a standoff technique for detection of vapor phase explosives. In addition, the Raman spectra of acetone, ethanol, and methanol were measured at the same wavelengths, and their influence on the spectrum from NM was investigated.

A Composite Detection and Disposal Scheme for Explosive Embedded in Building

The terrorists may embed explosives in the building, and then detonate them at a certain time. In recent years, the detection of this kind of explosive has been a new subject in anti-terrorism. Aiming to prevent this form of terrorist attack, this paper discusses some current explosive detection techniques and the way they may be used in the inspection and assessment of building. The techniques that have been studied are: ground penetration radar, harmonic radar, neutral technique and abrasive water jet cutting technology. Based on the results of analysis----an overall assessment scheme is proposed. This type of scheme has been proved to fit environment of reinforced concrete and to improve detection rate as well as for reduction of false rates too.

Microreactor-Based Synthesis of Molecularly Imprinted Polymer Beads Used for Explosive Detection

Molecularly imprinted polymer (MIP) beads based on acrylate formulations have been successfully synthesized in two different types of microreactors capable of generating spherical prepolymer droplets of controlled size in continuous segmented flow processes. After polymerizing and curing the droplets monodisperse acrylate particles have been obtained. Particle sizes have been adjusted in a wide range from 10 to 140 μm by choosing appropriate flow rates of the continuous and the disperse phase. By adding trinitrotoluene (TNT) as a template and PEG as a coporogen to the disperse phase MIP beads with TNT-selective sites and a sufficiently high porosity have been synthesized, as required, for explosive detection techniques.

Stand-off detection of trace explosives via resonant infrared photothermal imaging

We describe a technique for rapid stand-off detection of trace explosives and other analytes of interest. An infrared (IR) laser is directed to a surface of interest, which is viewed using a thermal imager. Resonant absorption by the analyte at specific IR wavelengths selectively heats the analyte, providing a thermal contrast with the substrate. The concept is demonstrated using trinitrotoluene and cyclotrimethylenetrinitramine on transparent, absorbing, and reflecting substrates. Trace explosives have been detected from particles as small as 10 μm.

X-ray scatter tomography for explosives detection

An account is given of three explosive detection techniques based on X-ray scatter tomography i.e. coherent scatter computed tomography, energy–dispersive X-ray diffraction tomography and Compton back-scatter imaging. Following an introduction to the physics of the underlying X-ray interaction phenomena, the principles on which these image-forming techniques are based are elaborated. A brief description is given of some of the parameters relevant to the X-ray scatter system design and of the optimisation of these parameters for the target application. Signal degradation owing to self-attenuation of the primary and scatter radiations and multiple scattering is discussed and procedures to correct for these effects are presented. The above techniques have been applied to the problem of identifying and detecting explosive material in airport baggage and buried land mines. Decision criteria needed to limit the number of “false alarms” are discussed. Representative results drawn from the fields of baggage inspection and mine clearance are given.

Neutron-based techniques for detection of explosives and drugs

Systematic measurements were carried out on the possible use of elastically backscattered Pu–Be neutrons combined with the thermal neutron reflection method for the identification of landmines and illicit drugs via the detection of H, C, N, and O elements as their major constituents. While our present results show that these methods are capable of indicating the anomalies in bulky materials and observation of the major elements, determination of the exact atom fractions needs further investigation.

Commercial Systems for the Direct Detection of Explosives for Explosive Ordnance Disposal Tasks

There are a number of Explosive Ordnance Disposal (EOD) tasks in which it is necessary to discriminate and identify UneXploded Ordnance (UXO) already detected by other means. What we seek is the capacity to characterize in a non-destructive way the munition's content, usually either explosive or inert (e.g., practice munition), if possible using a fairly mobile system and without direct contact. A number of existing technologies for the direct detection of explosives, applicable in EOD scenarios, are therefore characterized, and corresponding commercially available systems or advanced prototypes identified whenever possible. Some of the techniques are also useful for the detection of buried UXO or landmines, to which we refer whenever appropriate. We first concentrate on bulk explosive detection, in particular on neutron based systems exploiting gamma spectroscopy, which have the potential of detecting the explosive's nitrogen content and/or its other constituents (carbon, oxygen and hydrogen). Candidate systems exist, although most of them have as primary aim the discrimination of chemical munition. We then describe the application of trace explosive detection techniques, which seems to be less mature also due to the large number of parameters influencing the variables of interest (explosive vapor and particle concentration). Sampling is in this case of primary importance.